Note: Descriptions are shown in the official language in which they were submitted.
CA 02782695 2012-05-31
PF 62862
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Highly reactive, stabilized adhesive based on polyisocyanate
Description
The present invention relates to a highly reactive isocyanate component
comprising an
organic isocyanate having at least two isocyanate groups, a catalyst based on
an
organic metal compound and a compound which comprises an aromatic sulfonyl
isocyanate group. The present invention furthermore relates to a process for
the
production of lignocellulose-containing materials with the use of the highly
reactive
isocyanate component, such lignocellulose-containing materials and a sealant
comprising the highly reactive isocyanate component.
Materials based on lignocellulose are known. Important examples of
lignocellulose-
containing substances are wood parts, such as wood layers, wood strips,
woodchips or
wood fibers, it optionally also being possible for the wood fibers to
originate from wood
fiber-containing plants, such as flax, hemp, sunflowers, Jerusalem artichoke
or rape.
Starting materials for such wood parts or wood particles are usually timbers
from the
felling of forests, waste industrial timbers and used timbers and wood fiber-
containing
plants.
The treatment to give the desired lignocellulose-containing substances, such
as wood
particles, is effected by known processes, cf. for example M. Dunky, P. Niemt,
Holzwerkstoffe and Leime, pages 91-156, Springer Verlag Heidelberg, 2002.
Lignocellulose-containing moldings, also referred to here as wood-based
materials in
the case of wood as lignocellulose, are an economical and resource-protecting
alternative to solid wood and have become very important, in particular in
furniture
construction and as construction materials. As a rule, wood layers of
different
thickness, wood strips, woodchips or wood fibers from different woods serve as
starting
materials for wood-based materials. Such wood parts or wood particles are
usually
compressed at elevated temperature with natural and/or synthetic binders and
optionally with addition of further additives to give board-like or strand-
like wood-based
materials. Examples of such lignocellulose-containing moldings or wood-based
materials are medium density fiber boards (MDF), wood particle materials, such
as
particle boards and oriented strand boards (OSB), plywood, such as veneer
plywood,
and glued wood.
Binders used as a rule are formaldehyde-containing binders, for example urea-
formaldehyde resins or melamine-containing urea-formaldehyde resins. The
resins are
prepared by polycondensation of formaldehyde with urea and/or melamine. The
use of
such formaldehyde resins can lead to the presence of free formaldehyde in the
finished
wood-based material. By hydrolysis of the polycondensates, additional
formaldehyde
can be liberated. The free formaldehyde in the wood-based material and the
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formaldehyde liberated during the life of the wood-based material by
hydrolysis can be
released to the environment.
Above certain limits, formaldehyde may cause allergies, skin irritation,
irritation of the
respiratory tract and eye irritation in humans. The reduction of formaldehyde
emission
in components, especially in the interior region, is therefore an important
challenge.
For reducing or suppressing the formaldehyde emission, it is possible to use
aminoplast glues which have been prepared using little formaldehyde.
Furthermore, it
is possible to aftertreat the finished wood-based materials with so-called
formaldehyde
scavengers, such as compounds comprising amine groups. A further possibility
is the
application of a top layer to the wood-based material, the top layer being
obtained
using a glue to which larger amounts of melamine and/or urea have been added
as
formaldehyde scavengers.
Such measures are, however, still not completely satisfactory. The preparation
of the
aminoplast glues using less formaldehyde or the addition of formaldehyde
scavengers
to the aminoplast glue results in the glue hardening more slowly, which
prolongs the
residence times in the hot press and hence adversely affects the cost-
efficiency of the
production of the wood-based material.
DE-A 2 306771 (Deutsche Novopan GmbH) describes a process for the production
of
particle boards from, for example, woodchips to which binder has been added
and
which are sprinkled in at least three layers and then hot-pressed, a defined
phenol
resin being used as a binder for the top layer and, for example, isocyanate
being used
as a binder in the middle layer.
DE 28 32 509 B1 (Deutsche Novopan GmbH) describes particle boards having a
middle layer which was produced with urea-formaldehyde resin, isocyanate and
addition of urea and a top layer which was produced with urea-formaldehyde
resin and
added urea.
Advantages of the use of isocyanate as a binder are the high hydrolysis
stability of the
lignocellulose-containing material obtained. A disadvantage of the use of
isocyanates
as binders is their relatively high price. The cost-efficiency of using
isocyanates could
be increased by shorter residence times in the hot press.
It was therefore an object of the present invention to provide an even more
highly
reactive isocyanate component which is suitable as a binder for the production
of
lignocellulose-containing materials, reacts rapidly during the hot pressing
and
nevertheless can be stored for a long time at room temperature.
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The object according to the invention is achieved by a highly reactive
isocyanate
component comprising an organic isocyanate having at least two isocyanate
groups, a
catalyst based on an organic metal compound and a compound which comprises an
aromatic sulfonyl isocyanate group.
All organic isocyanates and prepolymers known to the person skilled in the
art,
preferably those known for the production of wood-based materials or
polyurethanes,
can be used as organic isocyanate having at least two isocyanate groups. Such
organic isocyanates and their preparation and use are described, for example,
in
Becker/Braun, Kunststoff Handbuch, 3rd revised addition, volume 7
"Polyurethane",
Hanser 1993, pages 17 to 21, pages 76 to 88 and pages 665 to 671.
Preferred organic isocyanates are oligomeric isocyanates having 2 to 10,
preferably 2
to 8, monomer units and on average at least one isocyanate group per monomer
unit.
A particularly preferred organic isocyanate is the oligomeric organic
isocyanate PMDI
("polymeric methylenediphenylene diisocyanate"), which is obtainable by
condensation
of formaldehyde with aniline and phosgenation of the isomers and oligomers
formed in
the condensation (cf. for example Becker/Braun, Kunststoff Handbuch, 3rd
revised
edition, volume 7 "Polyurethane", Hanser 1993, page 18, last paragraph to page
19,
second paragraph and page 76, fifth paragraph). The PMDI preferably has a
viscosity
at 25 C of 100 to 600, particularly preferably 150 to 300 mPa.s. It is also
possible to
use mixtures of organic isocyanates. PMDI products which are very suitable in
the
context of the present invention are the products of the LUPRANAT series of
BASF
SE, in particular LUPRANAT M 20 FB of BASF SE.
All known organic metal compounds which accelerate the reaction of isocyanates
with
compounds comprising hydroxyl groups, in particular with lignocellulose-
containing
substances, can be used as a catalyst based on an organic metal compound.
Examples of such organic metal compounds are organic tin compounds, such as
tin(II)
salts of organic carboxylic acids, such as tin(II) acetate, tin(II) octanoate,
tin(ll) ethyl-
hexanoate and tin(II) laurate, and the dialkyltin(IV) salts of organic
carboxylic acids,
such as dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate and
dioctyltin
diacetate, and bismuth carboxylates, such as bismuth(III) neodecanoate,
bismuth
2-ethylhexanoate and bismuth octanoate, or alkali metal salts of carboxylic
acids, such
as potassium acetate or potassium formate, and mixtures of these compounds
with
one another. Organic tin compounds, in particular tin mercaptides, such as
dimethyltin
or dioctyltin mercaptides, are preferably used.
The proportion of the catalyst based on an organic metal compound, relative to
the
total weight of the highly reactive isocyanate component, is preferably from
0.01 to
PF 62862 CA 02782695 2012-05-31
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0.3%, particularly preferably from 0.01 to 0.15% by weight and in particular
from 0.01 to
0.08% by weight.
Furthermore, the highly reactive isocyanate component according to the
invention also
comprises a compound which comprises an aromatic sulfonyl isocyanate group.
The
sulfonyl isocyanate group must to an aromatic system, for example to a phenyl
ring.
Preferably, the aromatic system comprises no further isocyanate groups. For
example,
para-toluenesulfonyl isocyanate may be used as a compound which comprises an
aromatic sulfonyl group.
The proportion of the compound which comprises an aromatic sulfonyl isocyanate
group, based on the total weight of the highly reactive isocyanate component,
is
preferably from 0.01 to 2.0% by weight, more preferably from 0.01 to 0.5% by
weight,
even more preferably from 1 to 5 times, particularly preferably from 2 to 4
times and in
particular from 2.5 to 3.5 times, the content of catalyst based on an organic
metal
compound.
In addition to said substances, the highly reactive isocyanate component may
have
further compounds which are usually present in an isocyanate component which
is
used as binder for the production of lignocellulose-containing materials.
These may be,
for example, customary additives, such as iron compounds, for example
iron(III)
chloride. If iron(III) chloride is used, the iron content, based on the total
weight of the
organic isocyanate, is usually from 10 to 100 mg/kg, preferably from 40 to 70
mg/kg. In
a further preferred embodiment, the iron content, based on the total weight of
the
organic isocyanate, is from 10 to 30 mg/kg.
For the production of the lignocellulose-containing materials, lignocellulose-
containing
substances are with a highly reactive isocyanate component according to the
invention
and then compressed in a mold at mold temperatures of from 40 to 250 C,
preferably
from 100 to 240 C and particularly preferably from 150 to 230 C.
The production of lignocellulose-containing materials according to the
invention,
preferably those in which the lignocellulose-containing particles are wood
particles, is
effected in a customary manner, as described in "Taschenbuch der Spanplatten
Technik" H.-J. Deppe, K. Ernst, 4th edition, 2000, DRW - Verlag Weinbrenner
GmbH &
Co., Leinfelden-Echterdingen, chapter 3.5.
The term lignocellulose is known to a person skilled in the art. Important
examples of
lignocellulose-containing particles are wood parts, such as wood layers, wood
strips,
woodchips or wood fibers, it being possible for the wood fibers optionally
also to
originate from wood fiber-containing plants, such as flax, hemp, sunflowers,
Jerusalem
artichoke or rape.
PF 62862 CA 02782695 2012-05-31
Wood particles, in particular wood fibers or woodchips, are preferred as
lignocellulose-
containing substances.
5 In addition to the highly reactive isocyanate component and the
lignocellulose-
containing substances, further binders usually used for the production of such
materials
can be used. These comprise, for example, customary binders prepared on the
basis
of polycondensates of formaldehyde and phenols, ureas or melamine. Such resins
and
their preparation are described, for example, in Ullmanns Enzyklopadie der
technischen Chemie, 4th, revised and extended edition, Verlag Chemie, 1973,
pages 403 to 424, "Aminoplaste", and Ullmann's Encyclopedia of Industrial
Chemistry,
Vol. A2, VCH Verlagsgesellschaft, 1985, pages 115 to 141, "Amino Resins", and
in
M. Dunky, P. Niemz, Holzwerkstoffe and Leime, Springer 2002, pages 251 to 259
(UF
resins) and pages 303 to 313 (MUF and UF with a small amount of melamine).
Furthermore, customary additives may be used. These comprise all additives
known to
a person skilled in the art, for example waxes, paraffin emulsion, flame-
retardant
additives, wetting agents, salts, but also inorganic or organic acids and
bases, for
example mineral acids, such as sulfuric acid, nitric acid, organic sulfonic
acids,
carboxylic acids, such as formic acid or acetic acid, or inorganic or organic
bases, for
example sodium hydroxide (aqueous or as such), calcium oxide or calcium
carbonate
(each aqueous or as such) or ammonia, aqueous or as such. These additives can
be
added in an amount of from 0 to 20% by weight, preferably from 0 to 5% by
weight, in
particular from 0 to 1 % by weight, based on the dry mass of the
lignocellulose-
containing substances. Particularly preferably, the proportion of water is
minimized.
Thus, the proportion of water is preferably less than 2% by weight,
particularly
preferably less than 1 % by weight and in particular less than 0.5% by weight,
based in
each case on the total weight of all starting materials used for the
production of the
lignocellulose-containing materials, including residual moisture present in
the
lignocellulose-containing substances.
Prior to compression, the lignocellulose-containing substances, preferably
wood
particles, particularly preferably woodchips or wood fibers, are glue-coated
with the
highly reactive isocyanate component according to the invention. Such so-
called glue-
coating methods are known for the production of conventional wood-based
materials
with customary aminoplast resins and are described, for example, in
"Taschenbuch der
Spanpiatten Technik" H.-J. Deppe, K. Ernst, 4th edition, 2000, DRW - Verlag
Weinbrenner GmbH & Co., Leinfelden-Echterdingen, chapter 3.3.
Preferably, the highly reactive isocyanate component and the optionally used
further
binders and/or customary additives are not mixed before being brought into
contact
with the lignocellulose-containing substances. All components may be added
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simultaneously to the lignocellulose-containing substances. In a preferred
embodiment,
the highly reactive isocyanate component according to the invention is added
as the
last component to the lignocellulose-containing substances.
The procedure is optionally effected in a plurality of layers. These layers
may differ in
the type and size of the lignocellulose-containing substances, the amount and
the type
of the binder used or of the additives used.
The thickness of the multilayer lignocellulose-containing materials according
to the
invention, preferably of the board-like moldings, varies with the field of use
and is as a
rule in the range from 0.5 to 300 mm, preferably in the range from 10 to 200
mm, in
particular from 12 to 100 mm.
The thickness ratios of the layers of the multilayer lignocellulose-containing
moldings
according to the invention, preferably of the board-like moldings, are
variable. Usually,
the outer layers, also referred to as covering layers, individually or in
total, are thinner
than the layer or layers of the middle layers(s).
The mass an individual covering layer is usually in the range from 5 to 30% by
weight,
preferably from 10 to 25% by weight, of the total mass of the multilayer
lignocellulose-
containing molding according to the invention.
The invention furthermore relates to a lignocellulose-containing material
obtainable by
a process according to the invention. Such a lignocellulose-containing
material
according to the invention can be used, for example, for the production of
articles of
furniture and furniture parts, packaging materials, in house building or in
vehicles, such.
as cars, buses, trucks, boats and aircraft. It has a low formaldehyde emission
and is
particularly stable to hydrolysis.
The highly reactive isocyanate component according to the invention is
distinguished
by good storability at room temperature and rapid curing in contact with
groups reactive
towards isocyanate or in contact with moisture, for example at elevated
temperature.
Thus, the highly reactive isocyanate component according to the invention can
also be
used for further purposes, for example as a sealant. Such sealants can be
used, inter
alia, as a moisture-curing sealants, for example in the construction industry.
Here, the
curing time can also be substantially shortened at room temperature compared
with
known sealants.
The invention is illustrated below with reference to examples.
Storage stability:
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The storage stability of a polymer MDI isocyanate component having a viscosity
of
260 mPa.s at 20 C and an iron content of 25 mg/kg and a content of 0.04% by
weight
of the tin catalyst Fomrez .UL32 from Witco is tested. For this purpose the
polymer
MDI isocyanate component is stored without further additives at 25 C
(comparison)
and with 0.12% by weight, based on the total weight of the mixture, of para-
toluenesulfonyl isocyanate at 25 C (example 1) and at 50 C (example 2). The
viscosity
of the mixtures in mPa.s as a function of the duration of storage is shown in
table I and
figure 1.
Table 1
Comparison Example 1 (25 C) Example 2 (50 C)
0 days 268 mPa.s 268 mPa.s 268 mPa.s
7 days 276 mPa.s 267 mPa.s 262 mPa.s
11 days 280 mPa.s 266 mPa.s 265 mPa.s
16 days 296 mPa.s 267 mPa.s 266 mPa.s
22 days 322 mPa.s 270 mPa.s 267 mPa.s
29 days 385 mPa.s 270 mPa.s 285 mPa.s
36 days 432 mPa.s 270 mPa.s 292 mPa.s
40 days - 272 mPa.s 297 mPa.s
60 days - 270 mPa.s 305 mPa.s
80 days - 268 mPa.s 310 mPa.s
100 days - 268 mPa.s 315 mPa.s
Table 1 shows that the viscosity of the isocyanate component without para-
toluenesulfonyl isocyanate increases within a few days even at 25 C. On the
other
hand, the viscosity of the isocyanate component with para-toluenesulfonyl
isocyanate,
which was stored at 25 C, is still as the same as the starting viscosity even
after
storage for 100 days, and the viscosity) n crease of the isocyanate component
with
para-toluenesulfonyl isocyanate, stored at 50 C, is also substantially slowed
down
compared with the comparative example at 25 C.
The reactivity of the isocyanate component as a function of the catalyst
concentration
is shown in table 2. The tests were carried out on the basis of the standard
EN 319.
OSB (Oriented Strand Boards) wood fibers were mixed with 4% of isocyanate
mixture
and pressed at a press plate temperature of 220 degrees with different
pressing factors
from 7 to 9 sec/mm (staggered in 0.5 sec/mm steps). Thereafter, test specimens
measuring 50 x 50 x 14 mm were cut out and were stored for 7 days under
standard
climatic conditions. The transverse tensile strength according to EN 319 was
determined on these test specimens. The composition of the isocyanate
component in
comparative experiment 2 corresponded to that from comparison 1, no catalyst
having
been used. The composition of the isocyanate component in example 2
corresponded
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to example 1, 0.06% by weight of catalyst having been used instead of 0.04% by
weight.
Table 2
Pressing time in s/mm Comparison 2 Example 3
thickness
7 0.05 N/mm2 0.75 N/mmz
7.5 0.3 N/mmz 0.75 N/mm2
8 0.55 N/mm2 0.78 N/mm2
8.5 0.8 N/mmz 0.80 N/mm2
9 1.0 N/mmz 0.80 N/mm2
Table 2 shows that a high transverse tensile strength is achieved with the use
of
example 1 after pressing times of only 7 seconds per mm thickness, while
corresponding values of the transverse tensile strength are achieved for
comparison
example 2 only after 8.5 seconds/mm.
